I had an '86 Accord in the family, and it required more repairs than the '86 300E.
At 150K miles and 12 years of age, the Honda was no longer worth keeping. Too much rust, and too many problems. I did not find common parts to be much cheaper, though they were more likely to be in stock at local part stores.
At 190k and 16 years, the 300E shows its age somewhat, but has very little corrosion, and the motor is still strong and smooth.
Body hardware, and interior bits holdup so much better. These little things add up to make a difference. Components tend to be impressively 'overbuilt' in general. It is also much easier to service. That Accord with its transverse engine was a nightmare- you would need minature hands to do anything.
Some MB parts are indeed pricey, but mailorder comes to the rescue. Most common wear items are readily available through aftermarket/gray market distribution channels with OEM goods, and suprisingly reasonable. If you do your own service, it's not so bad. If you are subjected to 'list prices' when you hire service out, things can indeed be worse on an MB than a Honda.
I cannot comment on the Legend's reliability, though I drove a 1990 model some distance. It was solid and comfortable enough. I found the suspension to be way too soft for my taste. It was not particulary powerful either, lacking steam for passing maneuvers where the MB excels.
Good luck with your shopping.
1986 300E 5-Speed 240k mi.